External circulation ball screw

ABSTRACT

An external circulation ball screw includes: a screw shaft; a nut sleeved on the screw shaft and including a through hole having an opening end; and a return member mounted on the nut, and including a return groove having a return section and a continuation section, one end of the return section connected to the through hole including a connecting end which abuts against the opening end. The opening end and the connecting end are non-tangentially connected, the return section circles around a reference point, the outer wall surface of the return section is arc-shaped and centered on the reference point, a distance between the outer wall surface and the reference point is a radius of curvature, and the radius of curvature is greater than or equal to 1.2 times the ball diameter, but is less than or equal to 1.5 times the ball diameter.

BACKGROUND Field of the Invention

The present invention relates to a ball screw, and more particularly to an external circulation ball screw.

Description of Related Art

In order to cope with the current automotive electronics and consumer electronics products, the ball screw includes been developed towards the direction of miniaturization. However, in the existing design of the internal return plate, there is generally a height difference between the nut and the return plate, so that when the diameter of the ball is small, it will produce noticeable unsmoothness.

The existing tangential external circulation ball screw, as shown in FIG. 1, includes a nut 70, a return upper cover 80 combined with the nut 70, and a plurality of balls 90 movable between the nut 70 and the return upper cover 80. The nut 70 is includes two through holes 71, and the extending direction of the through holes 71 as a moving direction Z. The return upper cover 80 includes a return passage 81 which communicates with the through holes 71, so that the balls 90 can circulate. The return passage 81 and the through holes 71 are connected in a tangential manner. The return passage 81 includes a return section 811 and an extending section 812 that are connected, because the return passage 81 and the through holes 71 are connected in a tangential manner, and the inner space of the return section 811 is relatively large. Therefore, when the balls 90 enter the return section 811 through the through holes 71, the ball 90 will inertially hit the corresponding upper edge of the wall surface 811A of the return section 811, so that, after the balls 90 hit the wall surface 811A of the return section 811, the component of the reaction force along the moving direction Z is relatively large, causing the front ball 90 and the rear ball 90 to squeeze, resulting in the disadvantages of ball squeezing and large impact force.

SUMMARY

The present invention provides an external circulation ball screw, the main objective of which is to provide a miniature ball screw that makes the balls flow smoothly and avoid the problem of ball squeezing.

To achieve the above objective, the external circulation ball screw provided by the present invention comprises:

a screw shaft;

a nut sleeved on the screw shaft, a ball passage being formed between the nut and the screw shaft, the nut including at least one through hole in communication with is the ball passage, the at least one through hole including an opening end;

a plurality of balls disposed and circulating in the ball passage, and each of the balls having a ball diameter; and

a return member mounted on the nut, and including a return groove in communication with the at least one through hole, the return groove including a return section in communication with the at least one through hole, one end of the return section connected to the at least one through hole including a connecting end which abuts against the opening end, wherein the opening end and the connecting end are connected in a non-tangential manner, the return section circles around a reference point, the return section corresponds to an outer wall surface, the outer wall surface is arc-shaped and centered on the reference point, a distance between the outer wall surface and the reference point is defined as a radius of curvature, and the radius of curvature is greater than or equal to 1.2 times the ball diameter, but is less than or equal to 1.5 times the ball diameter.

It can be learned from the above that the present invention mainly defines that the radius of curvature R is greater than or equal to 1.2 times the ball diameter but is less than or equal to 1.5 times the ball diameter, and the opening end and the connecting end are connected in a non-tangential manner, which can effectively reduce the problem of ball squeezing caused by the unsmooth flow of the balls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional ball screw in which the return passage and the is through holes are connected in a tangential manner;

FIG. 2 is an exploded view of an external circulation ball screw in accordance with the present invention;

FIG. 3 is a schematic top view of the external circulation ball screw in accordance with the present invention;

FIG. 4 is a schematic diagram of the invention showing the non-tangential connection between the through holes and the return groove;

FIG. 5A shows the impact force data graph, under the condition that the conventional return passage and the through holes are connected in a tangential manner, the radius of curvature is 0.7 mm, where Each fold line in the coordinates represents the impact force generated by each ball at different time points, the horizontal axis in the figures represents time, the unit is second (S), and the vertical axis represents the impact force, and the unit of impact force is Newton (N);

FIG. 5B shows the impact force data graph, under the condition that the conventional return passage and the through holes are connected in a tangential manner, and the radius of curvature is 0.8 mm;

FIG. 5C shows the impact force data graph, under the condition that the conventional return passage and the through holes are connected in a tangential manner, and the radius of curvature is 0.9 mm;

FIG. 5D shows the impact force data graph of the invention, under the condition that the through holes and the return groove are connected non-tangentially, and the radius of curvature is 0.8 mm;

FIG. 5E shows the impact force data graph of the invention, under the condition that the through holes and the return groove are connected non-tangentially, and the radius of curvature is 0.85 mm;

FIG. 5F shows the impact force data graph of the invention, under the condition that the through holes and the return groove are connected non-tangentially, and the radius of curvature is 0.9 mm; and

FIG. 5G shows the impact force data graph of the invention, under the condition that the through holes and the return groove are connected non-tangentially, and the radius of curvature is 1.0 mm

DETAILED DESCRIPTION

The present invention provides an external circulation ball screw. In one of the embodiments, please refer to FIGS. 2-4, the invention comprises: a screw shaft 10, a nut 20, a plurality of balls 30, and a return member 40.

-   -   The screw shaft 10 extends along an axis L, an outer         circumferential surface of the screw shaft 10 includes an         external thread groove 11, and the axis L defines an axial         direction X.     -   The nut 20 is sleeved on the screw shaft 10, and includes: an         insertion hole 20 a for insertion of the screw shaft 10, an         inner surface 21 and an outer surface 22 opposite to each other.         The outer surface 22 is a flat surface. The inner surface 21         faces the insertion hole 20 a and includes an internal thread         groove 211 corresponding to the external thread groove 11. A         ball passage T1 is formed between the internal thread groove 211         and the external thread groove 11. The nut 20 includes two first         is thread holes 23 and two through holes 24, and the two first         thread holes 23 and the two through holes 24 penetrate the outer         surface 22. The ball passage T1 communicates with the two         through holes 24, the two through holes 24 penetrate the outer         surface 22 at an opening end 241, and an extending direction of         each of the through holes 24 is a vertical direction Y.     -   A plurality of balls 30 are disposed and circulate in the ball         passage T1, and each of the balls 30 has a ball diameter BD. In         a specific embodiment, the ball diameter BD is between 1.0 mm         and 0.4 mm     -   A return member 40 is mounted on the outer surface 22 of the nut         20, and includes a bearing surface 40A facing the outer surface         22. The bearing surface 40A is flat, and includes a return         groove 41. The return groove 41 and the two through holes 24         jointly form a return path T2, and the return path T2 is in         communication with the ball passage T1. The return groove 41         includes a return section 411, a continuation section 412 and a         outlet section 413 which are connected in sequence. The return         section 411 communicates with one of the through holes 24, and         the outlet section 413 communicates with another one of the         through holes 24. One end of the return section 411 connected to         the through hole 24 includes a connecting end 411A which abuts         against the opening end 241, and another end of the return         section 411 is connected to the continuation section 412. An         extending direction of the return section 411 includes the         components of the axial direction X and the vertical direction         Y, so that an outer wall surface 411B corresponding to the         return section 411 is arc-shaped, the return section 411 circles         around a reference point A, and the outer wall surface 411B is         is centered on the reference point A. A distance between the         outer wall surface 411B and the reference point A is a radius of         curvature R, and the radius of curvature R is greater than or         equal to 1.2 times the ball diameter BD, but is less than or         equal to 1.5 times the ball diameter BD.     -   The opening end 241 and the connecting end 411A are connected in         a non-tangential manner, so that the return path T2 is a         non-tangential path.     -   As a result, since the connecting end 411A of the return section         411 of the return groove 41 and the opening end 241 of the         through hole 24 are connected in a non-tangential manner,         compared with the conventional tangential connection design,         when the radius of curvature R is the same, the inner space of         the return section 411 of the present invention is relatively         small, and the position where the balls 30 hit the outer wall         surface 411B of the return section 411 is closer to the         connecting end 411A, so that the component force along the axial         direction X of the reaction force of the ball 30 hitting the         outer wall surface 411B is relatively large. Therefore, the ball         30 in the front is less likely to be squeezed by the ball 30 in         the rear when entering the continuation section 412 along the         return section 411, so the impact force is relatively small,         which consequently can improve the smoothness of the return flow         of the balls.     -   The return member 40 further includes two second thread holes 43         located corresponding to the two first thread holes 23         respectively, and two locking members 50 are respectively         inserted through the first thread holes 23 and the second thread         holes 43 to lock the return member 40 on the nut 20.     -   Preferably, the return member 40 further includes two extending         portions 42 which extend from the bearing surface 40A, one of         the extending portions 42 is adjacent to the return section 411,         another one of the extending portions 42 is adjacent to the         outlet section 413, and the extending portions 42 are         respectively inserted into the through holes 24.     -   The above is the configuration description of the main         components of each embodiment of the present invention. As for         the effects of the present invention, the description is as         follows:     -   The computer simulates the impact force on the return passage 81         when the balls 90 pass through the conventional return upper         cover 80. Please refer to FIGS. 5A to 5C, which show the impact         force caused by the balls 90 when passing through the return         passage 81, under the condition that the conventional return         passage 81 and the through hole 71 are connected in a tangential         manner, and the ball diameter is 0.6 mm Each fold line in the         coordinates represents the impact force generated by each ball         90 at different time points in the return passage 81, the         horizontal axis in the figures represents time, the unit is         second (S), and the vertical axis represents the impact force,         the unit of impact force is Newton (N). When the radius of         curvature is 0.7 mm, please refer to FIG. 5A, the average impact         force of the balls 90 is 13N, and the maximum impact force of         the balls 90 is 35.37N. When the radius of curvature is 0.8 mm,         please refer to FIG. 5B, the average impact force of the balls         90 is 1.5N, and the maximum impact force of the balls 90 is         3.09N. When the radius of curvature is 0.9 mm, please refer to         FIG. 5C, the average impact force of the balls 90 is 3.7N, and         is the maximum impact force of the balls 90 is 6.47N.     -   For computer simulation of the impact force on the return groove         41 caused by the balls 30 when passing through the return member         40 of this invention, please refer to FIGS. 5D to 5F, which show         the impact force caused by the balls 30 when passing through the         return groove 41, under the condition that the through holes 24         and the return groove 41 of this invention are connected in a         non-tangent manner, and the ball diameter BD is 0.6 mm. Each         fold line in the coordinates represents the impact force         generated by each ball 30 at different time points in the return         groove 41, the horizontal axis represents time, the unit is         second (S), the vertical axis represents impact force, and the         unit of impact force is Newton (N). When the radius of curvature         R is 0.8 mm, please refer to FIG. 5D, the average impact force         of the balls 30 is 0.29N, and the maximum impact force of the         balls 30 is 0.75N. When the radius of curvature R is 0.85 mm,         please refer to FIG. 5E, the average impact force of the balls         30 is 0.26N, and the maximum impact force of the balls 30 is         0.89N. When the radius of curvature R is 0.9 mm, please refer to         FIG. 5F, the average impact force of the balls 30 is 0.38N, and         the maximum impact force of the balls 30 is 0.66N.     -   Please also refer to FIG. 5G, where the through holes 24 and the         return groove 41 are connected non-tangentially, and the ball         diameter BD is 0.6 mm However, when the radius of curvature R is         1.0 mm, the condition that the radius of curvature R is less         than or equal to 1.5 times the ball diameter BD can no longer be         satisfied, so the test result shows that the balls 30 will be         stuck and cannot flow back smoothly.     -   In summary, under the condition that the radius of curvature R         is 0.8 mm, the average impact force of the balls 30 is only         0.29N when the through holes 24 and the return groove 41 are         connected in a non-tangential manner, and the average impact         force of the ball 90 is increased to 1.5N when the return         passage 81 and the through holes 71 are connected in a         tangential manner. In addition, under the condition that the         radius of curvature R is 0.9 mm, the average impact force of the         balls 30 is only 0.38N when the through holes 24 and the return         groove 41 are connected in a non-tangential manner, and the         average impact force of the balls 90 is increased to 3.7N when         the return passage 81 and the through holes 71 are connected in         a tangential manner.     -   Based on the foregoing, the present invention mainly defines         that the radius of curvature R is greater than or equal to 1.2         times the ball diameter BD but is less than or equal to 1.5         times the ball diameter BD, and the opening end 241 and the         connecting end 411A are connected in a non-tangential manner,         which can effectively reduce the problem of ball squeezing         caused by the unsmooth flow of the balls 30. 

What is claimed is:
 1. An external circulation ball screw comprising: a screw shaft; a nut sleeved on the screw shaft, a ball passage being formed between the nut and the screw shaft, the nut including at least one through hole in communication with the ball passage, the at least one through hole including an opening end; a plurality of balls disposed and circulating in the ball passage, and each of the balls having a ball diameter; and a return member mounted on the nut, and including a return groove in communication with the at least one through hole, the return groove including a return section in communication with the at least one through hole, one end of the return section connected to the at least one through hole including a connecting end which abuts against the opening end, wherein the opening end and the connecting end are connected in a non-tangential manner, the return section circles around a reference point, the return section corresponds to an outer wall surface, the outer wall surface is arc-shaped and centered on the reference point, a distance between the outer wall surface and the reference point is defined as a radius of curvature, and the radius of curvature is greater than or equal to 1.2 times the ball diameter, but is less than or equal to 1.5 times the ball diameter.
 2. The external circulation ball screw as claimed in claim 1, wherein the ball diameter is between 1.0 mm and 0.4 mm.
 3. The external circulation ball screw as claimed in claim 1, wherein the return groove includes a continuation section and a outlet section, another end of the return section is connected to the continuation section, the continuation section is connected to the outlet section, the number of the at least one through hole is two, and the outlet section is in communication with another one of the two through holes.
 4. The external circulation ball screw as claimed in claim 1, wherein the nut includes an insertion hole for insertion of the screw shaft, the screw shaft includes an external thread groove, the nut includes an inner surface and an outer surface opposite to each other, the inner surface faces the insertion hole and includes an internal thread groove corresponding to the external thread groove, the ball passage is formed between the internal thread groove and the external thread groove, the return member is mounted on the outer surface of the nut, and the at least one through hole penetrates the outer surface at the opening end.
 5. The external circulation ball screw as claimed in claim 1, wherein the nut includes two first thread holes, the return member includes two second thread holes, the two second thread holes are located corresponding to the two first thread holes respectively, and two locking members are respectively inserted through the first thread holes and the second thread holes. 